1. Field of the Invention
The present invention relates to an improved process for producing a 4,6-bis(difluoromethoxy)-2-alkylthiopyrimidine which is useful as an intermediate for agricultural chemicals.
2. Discussion of Background
Heretofore, Japanese Unexamined Patent Publications No. 218378/1985 and No. 281869/1987 have disclosed processes for producing 4,6-bis(difluoromethoxy)-2-methylthiopyrimidine. According to the former process, a base is charged first using dioxane as the solvent for reaction, and then monochlorodifluoromethane and 2-methylthiobarbituric acid are reacted, whereupon the organic layer is separated and recovered, and dioxane is added again to the aqueous phase, and then the mixture is again reacted with the monochlorodifluoromethane, whereupon the organic layer is separated and recovered. This operation is repeated, and then the organic layers are put together, and the desired product is recovered by a usual method. However, the yield of the desired product according to this process is as low as 25%, and therefore, the process can hardly be qualified as an industrial process.
On the other hand, in the latter process, 4-chloro-6-hydroxy-2-methylthiopyrimidine as the starting material is first reacted with monochlorodifluoromethane to obtain 4-chloro-6-difluoromethoxy-2-methylthiopyrimidine, then this product was reacted with sodium nitrite in dimethylformamide t obtain 4-hydroxy-6-difluoromethoxy-2-methylthiopyrimidine, which is further reacted with monochlorodifluoromethane in dioxane in the presence of potassium hydroxide to obtain desired 4,6-bis(difluoromethoxy)-2-methylthiopyrimidine at a yield of 50%. However, this process also involves long process steps and is very cumbersome, and as such, it is not suitable as an industrial process.